Engine RPM is different at the same hwy speeds. Not an O.D. issue! (1 Viewer)

[leonard_nemoy]

I've noticed on both my 91 and 97 that something weird happens with my tach but only when driving highway speeds in windy conditions. The needle will jump up and down randomly by about 100 - 200 rpm's.

The first time I thought my transmission was going bad or something but I have since realized it's just something with the tach because the rpm's are not changing at all while the tach just jumps up and down randomly.

 

[alia176]

You folks are giving me some great info, thank you for that. First and foremost, let me verify my tach with obd when this is happening. I've done this in the past and they both matched, but night now I need to pay more attention.

I'll also hook up techstream when I drive the 80 and poke around to see if anything stands out. There might be a fault code that may come to light, who knows.

I know Kevin (ToolsRUs <RIP) did a great write-up on increasing the line pressure for a tighter shift and I'm now wondering if he was talking about the lockup logic. Since I'm turboed, I was wanting to do this eventually.

 

[Malleus]

You folks are giving me some great info, thank you for that. First and foremost, let me verify my tach with obd when this is happening. I've done this in the past and they both matched, but night now I need to pay more attention.

I'll also hook up techstream when I drive the 80 and poke around to see if anything stands out. There might be a fault code that may come to light, who knows.

I know Kevin (ToolsRUs <RIP) did a great write-up on increasing the line pressure for a tighter shift and I'm now wondering if he was talking about the lockup logic. Since I'm turboed, I was wanting to do this eventually.

Increasing line pressure has little or nothing to do with torque converter lockup. It either happens or it doesn't. That was the point of my (very long winded) posts. Kevin's point was to change the shift "feel" from the soft shift that Toyota purposely designed into the system (which delays the shift from one gear to another to prevent jerking the truck with the driveline) to something that would shift quicker between gears, to improve trail manners.

As I noted above, if you don't have the fault codes, you very likely don't have a torque converter problem. And if you do, the only way to verify that is to pull the torque converter and manually check the clutch operation.

 

[alia176]

Increasing line pressure has little or nothing to do with torque converter lockup. It either happens or it doesn't. That was the point of my (very long winded) posts. Kevin's point was to change the shift "feel" from the soft shift that Toyota purposely designed into the system (which delays the shift from one gear to another to prevent jerking the truck with the driveline) to something that would shift quicker between gears, to improve trail manners.

As I noted above, if you don't have the fault codes, you very likely don't have a torque converter problem. And if you do, the only way to verify that is to pull the torque converter and manually check the clutch operation.

Thanks again for the explanation.

 

[lumbee1]

My Cruiser was slipping in and out of lockup on a trip last year. Oddly enough expansion joints in the road caused it to change from locked up to not locked up which confused me further.

With the help of folks on this forum, it was determined that my brake pedal indicator switch under the dash was out of adjustment. When the brake switch was not activated, lockup occurred normally. When the brake switch activated (brake lights came on), lockup was deactivated. The switch was just far enough out of adjustment that bumps in the road would trigger it.

 

[alia176]

My Cruiser was slipping in and out of lockup on a trip last year. Oddly enough expansion joints in the road caused it to change from locked up to not locked up which confused me further.

With the help of folks on this forum, it was determined that my brake pedal indicator switch under the dash was out of adjustment. When the brake switch was not activated, lockup occurred normally. When the brake switch activated (brake lights came on), lockup was deactivated. The switch was just far enough out of adjustment that bumps in the road would trigger it.

This is a great clue and I mentioned previously that my CC (cruise control) doesn't get cancelled by the brake light pedal switch malfunctioning. However, I'll still do a continuity check just to rule it out. For all I know, I might've replaced it already as I've had this 80 for 18 years.

 

[lumbee1]

This is a great clue and I mentioned previously that my CC (cruise control) doesn't get cancelled by the brake light pedal switch malfunctioning. However, I'll still do a continuity check just to rule it out. For all I know, I might've replaced it already as I've had this 80 for 18 years.

It might just need to be adjusted. Really simple to do.

 

[sbman]

On my cruiser, I can clearly hear the lockup in the shift sequence.

With the engine warm, you should hear and feel all the shifts and the lock up; 1,2,3,4. After a short bit of light throttle cruising in 4th at >50mph (I thought it was 45, but the manual postings indicate 50), you'll hear and see it drop RPM one more time when the converter locks up. I can hear it and feel it unlock when you press the accelerator for more power, but not far enough to make it downshift into 3rd. I wasn't aware of the brake switch interaction, that's some useful info. You could gently press the brake pedal with your left foot once you've heard it lock and see if it unlocks, and also get a sense of how far down the brake pedal has to go to get it to unlock. Something I'll try on mine now just to see it work.

Of course if it doesn't ever lock then you have all of the troubleshooting steps in the FSM to work through.

 

[love mud 99]

So you mention coolant temperature has been modified to reflect real world temps, on the top picture what is the actual coolant temperature reading? Also skimming through the post I don't see if you answered why is the check engine light on?

 

[landtank]

First and foremost, let me verify my tach with obd when this is happening. I've done this in the past and they both matched,

the tach signal is generated on the ECU and not from the igniter like most vehicles. I doubt that they will ever be different.

 

[alia176]

It might just need to be adjusted. Really simple to do.

View attachment 3402756

My biggest clue is that my CC isn't getting cancelled so that tells me the adjustment is good but it's easy enough to check. I also lead wheeling trips and nobody has mentioned about the tail lights coming on randomly on the hwy or anything.